2,3-Dihydrofarnesal is known as a flavor and/or fragrance substance characterized in an aroma with a floral note (Japanese Patent Application Publication No. Hei 8-3092). 2,3-Dihydrofarnesal is known to be present in animals and plants in the natural world. For example, 2,3-Dihydrofarnesal is known to be present in an extract of Orchids (Aerides jarckianum), flower scent components of Citrus limon (Phytochemical Analysis (1997), 8(4), pp. 159-166), pheromone components of Bumblebees and Cuckoo Bumblebees (Chirality (2004), 16(4), pp. 228-233), and the like.
Moreover, 2,3-dihydrofarnesal also serves as an important raw material for (6E)-2,3-dihydrofarnesal, which has antimicrobial activity and which is useful as a muguet flavor and/or fragrance (Japanese Patent Application Publication No. Hei 8-245979).
As an example of synthesis of 2,3-dihydrofarnesal in an optically active form, a report is known in which (2E,6E)-farnesal is subjected to asymmetric hydrogen transfer reaction to synthesize (3R)-2,3-dihydrofarnesal (Angewnate Chemie, International Edition (2006), 45(25), pp. 4193-4195). Actually, however, (2Z,6E)-farnesal used as the raw material has to be separated and purified from a mixture of geometrical isomers, (2E,6E)-farnesal and (2Z,6E)-farnesal, by fine distillation. Furthermore, the asymmetric hydrogen transfer reaction of (2E,6E)-farnesal for obtaining the optically active 2,3-dihydrofarnesal requires an expensive and special asymmetric ligand.
Meanwhile, as an example of synthesis of 2,3-dihydrofarnesal in a racemic form, a report is known in which (2Z,6E)-dihydrofarnesyl allylamine is subjected to isomerization reaction using bis-(α,α′-diphenylphosphino)-o-xylylene as a ligand to obtain (6E)-dihydrofarnesyl enamine in a racemic form, which is subsequently hydrolyzed using acetic acid to synthesize (6E)-dihydrofarnesal (Japanese Patent Application Publication No. Sho 58-4748). However, in this conventional method, the ligand used for the reaction is not an optically active isomer. The report does not describe application to (2E,6E)-dihydrofarnesyl amine, which is a geometrical isomer, at all. Moreover, this report neither describes at all nor suggests which optically active isomer is formed by the isomerization reaction using an optically active isomer as the ligand in combination with the substrate, (2Z,6E)-isomer or (2E,6E)-isomer. Moreover, a method for obtaining (2Z,6E)-dihydrofarnesyl allylamine or the chemical purity thereof is not described. Hence, this report does not describe how to obtain (2Z,6E)-dihydrofarnesyl amine with a high chemical purity. Moreover, this report neither describes at all nor suggests how to obtain (2E,6E)-dihydrofarnesyl amine with a high chemical purity.